Routing devices within a network, often referred to as routers, maintain routing information that describes available routes through the network. Routers use routing protocols to exchange and accumulate topology information that describes the network. This allows a router to construct its own routing topology map of the network. Upon receiving an incoming packet, the router examines information within the packet and forwards the packet in accordance with the accumulated topology information.
Packet-based networks utilize label switching protocols for traffic engineering and other purposes. Multi-Protocol Label Switching (MPLS) is a mechanism used to engineer traffic patterns within Internet Protocol (IP) networks according to the routing information maintained by the routers in the network. By utilizing MPLS protocols, such as the Resource Reservation Protocol with Traffic Engineering extensions (RSVP-TE) or Label Distribution Protocol (LDP), label switching routers can forward traffic along a particular path through a network to a destination device, i.e., a Label Switched Path (LSP), using labels prepended to the traffic.
An LSP defines a distinct path through the network to carry MPLS packets from the source device to a destination device. Each router along a LSP allocates a label in association with the destination and propagates the label to the closest upstream router along the path. Routers along the path add (push), remove (pop), or swap the labels and perform other MPLS operations to forward the MPLS packets along the established path.